1. Field of the Invention
The present invention relates to a method and device for position detection, and more particularly, to a method and device for position detection using mutual-capacitance detection in combination with self-capacitance detection.
2. Description of the Prior Art
Touch displays have been widely used in the various electronic devices. One approach is to employ a touch sensitive panel to define a 2-D touch area on the touch display, where sensing information is obtained by scanning along horizontal and vertical axes of the touch panel for determining the touch or proximity of an external object (e.g. a finger) on or near the touch panel. U.S. Pat. No. 4,639,720 discloses a capacitive touch display.
Sensing information can be converted into a plurality of continuous signal values by an analog-to-digital converter (ADC). By comparing signal values before and after the touch or approaching of the external object, the location touched or approached by the external object can be determined.
Generally, a controller controlling the touch panel will first obtain sensing information when there is no external object touching or approaching as a baseline. For example, in a capacitive touch panel, each conductive line corresponds to a respective baseline. The controller determines whether there is an external object touching or approaching by comparing sensing information obtained subsequently with the baseline, and further determines the position of the external object. For example, when there is no external object touching or approaching the touch panel, subsequent sensing information with respect to the baseline will be or close to zero. Thus, the controller can determine whether there is an external object touching or approaching by determining whether the sensing information with respect to the baseline is or close to zero.
As shown in FIG. 1A, when an external object 12 (e.g. a finger) touches or approaches a sensing device 120 of a touch display 10, sensing information of sensors 140 on an axis (e.g. x axis) is converted into signal values as shown in FIG. 1B. Corresponding to the appearance of the finger, the signal values show a waveform or finger profile. The location of the peak 14 of the finger profile indicates the position touched or approached by the finger.
Since sensors on a touch panel are not densely disposed, i.e. there are gaps between the sensors, as shown in FIG. 5A (in a single dimension, for example). Thus, when a finger touches a fourth sensor on the touch panel, a corresponding touch related sensing information is detected (solid line). Meanwhile, the signal value detected by the fourth sensor is the maximum value, which is also the peak of this touch related sensing information.
Thereafter, when the finger gradually moves to the right, it will press against a position without any disposed sensor, e.g. between the fourth and fifth sensors. The touch related sensing information detected now is as shown by the dotted line. The peak of the touch related sensing information cannot be directly detected by the sensors, but position detection is required to calculate the position of the waveform peak. Since the sensors are not densely disposed, when a finger moves on a touch panel in a constant velocity in a certain dimension (X or Y direction), the touch panel displays the path of the moving finger in a non-constant velocity.
From the above it is clear that prior art still has shortcomings. In order to solve these problems, efforts have long been made in vain, while ordinary products and methods offering no appropriate structures and methods. Thus, there is a need in the industry for a novel technique that solves these problems.